Check this out, from the Roddenberry Vault. It's a completely different version of Star Trek IV, either set prior to Wrath of Khan or simply ignoring it and Search For Spock (it's set at the very end of the five year mission of the refitted Enterprise). Frustratingly, it doesn't have an end.

I'm happier with the STIV we got, but this is a fascinating what-might-have-been. One I'd never heard of before.